1 /* Support for dynamic linking code in static libc.
2 Copyright (C) 1996-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 /* This file defines some things that for the dynamic linker are defined in
20 rtld.c and dl-sysdep.c in ways appropriate to bootstrap dynamic linking. */
21
22 #include <string.h>
23 /* Mark symbols hidden in static PIE for early self relocation to work.
24 Note: string.h may have ifuncs which cannot be hidden on i686. */
25 #if BUILD_PIE_DEFAULT
26 # pragma GCC visibility push(hidden)
27 #endif
28 #include <errno.h>
29 #include <libintl.h>
30 #include <stdlib.h>
31 #include <unistd.h>
32 #include <sys/param.h>
33 #include <stdint.h>
34 #include <ldsodefs.h>
35 #include <dl-machine.h>
36 #include <libc-lock.h>
37 #include <dl-cache.h>
38 #include <dl-procinfo.h>
39 #include <unsecvars.h>
40 #include <hp-timing.h>
41 #include <stackinfo.h>
42 #include <dl-vdso.h>
43 #include <dl-vdso-setup.h>
44 #include <dl-auxv.h>
45 #include <dl-find_object.h>
46 #include <array_length.h>
47 #include <dl-symbol-redir-ifunc.h>
48
49 extern char *__progname;
50 char **_dl_argv = &__progname; /* This is checked for some error messages. */
51
52 /* Name of the architecture. */
53 const char *_dl_platform;
54 size_t _dl_platformlen;
55
56 int _dl_debug_mask;
57 int _dl_lazy;
58 int _dl_dynamic_weak;
59
60 /* If nonzero print warnings about problematic situations. */
61 int _dl_verbose;
62
63 /* We never do profiling. */
64 const char *_dl_profile;
65 const char *_dl_profile_output;
66
67 /* Names of shared object for which the RUNPATHs and RPATHs should be
68 ignored. */
69 const char *_dl_inhibit_rpath;
70
71 /* The map for the object we will profile. */
72 struct link_map *_dl_profile_map;
73
74 /* This is the address of the last stack address ever used. */
75 void *__libc_stack_end;
76
77 /* Path where the binary is found. */
78 const char *_dl_origin_path;
79
80 /* Nonzero if runtime lookup should not update the .got/.plt. */
81 int _dl_bind_not;
82
83 /* A dummy link map for the executable, used by dlopen to access the global
84 scope. We don't export any symbols ourselves, so this can be minimal. */
85 static struct link_map _dl_main_map =
86 {
87 .l_name = (char *) "",
88 .l_real = &_dl_main_map,
89 .l_ns = LM_ID_BASE,
90 .l_libname = &(struct libname_list) { .name = "", .dont_free = 1 },
91 .l_searchlist =
92 {
93 .r_list = &(struct link_map *) { &_dl_main_map },
94 .r_nlist = 1,
95 },
96 .l_symbolic_searchlist = { .r_list = &(struct link_map *) { NULL } },
97 .l_type = lt_executable,
98 .l_scope_mem = { &_dl_main_map.l_searchlist },
99 .l_scope_max = (sizeof (_dl_main_map.l_scope_mem)
100 / sizeof (_dl_main_map.l_scope_mem[0])),
101 .l_scope = _dl_main_map.l_scope_mem,
102 .l_local_scope = { &_dl_main_map.l_searchlist },
103 .l_used = 1,
104 .l_tls_offset = NO_TLS_OFFSET,
105 .l_serial = 1,
106 };
107
108 /* Namespace information. */
109 struct link_namespaces _dl_ns[DL_NNS] =
110 {
111 [LM_ID_BASE] =
112 {
113 ._ns_loaded = &_dl_main_map,
114 ._ns_nloaded = 1,
115 ._ns_main_searchlist = &_dl_main_map.l_searchlist,
116 }
117 };
118 size_t _dl_nns = 1;
119
120 /* Incremented whenever something may have been added to dl_loaded. */
121 unsigned long long _dl_load_adds = 1;
122
123 /* Fake scope of the main application. */
124 struct r_scope_elem _dl_initial_searchlist =
125 {
126 .r_list = &(struct link_map *) { &_dl_main_map },
127 .r_nlist = 1,
128 };
129
130 #ifndef HAVE_INLINED_SYSCALLS
131 /* Nonzero during startup. */
132 int _dl_starting_up = 1;
133 #endif
134
135 /* Random data provided by the kernel. */
136 void *_dl_random;
137
138 /* Get architecture specific initializer. */
139 #include <dl-procruntime.c>
140 #include <dl-procinfo.c>
141
142 size_t _dl_pagesize = EXEC_PAGESIZE;
143
144 size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
145
146 int _dl_inhibit_cache;
147
148 /* All known directories in sorted order. */
149 struct r_search_path_elem *_dl_all_dirs;
150
151 /* All directories after startup. */
152 struct r_search_path_elem *_dl_init_all_dirs;
153
154 /* The object to be initialized first. */
155 struct link_map *_dl_initfirst;
156
157 /* Descriptor to write debug messages to. */
158 int _dl_debug_fd = STDERR_FILENO;
159
160 ElfW(auxv_t) *_dl_auxv;
161 const ElfW(Phdr) *_dl_phdr;
162 size_t _dl_phnum;
163 uint64_t _dl_hwcap;
164 uint64_t _dl_hwcap2;
165
166 enum dso_sort_algorithm _dl_dso_sort_algo;
167
168 /* The value of the FPU control word the kernel will preset in hardware. */
169 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
170
171 /* Prevailing state of the stack. Generally this includes PF_X, indicating it's
172 * executable but this isn't true for all platforms. */
173 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
174
175 #if PTHREAD_IN_LIBC
176 list_t _dl_stack_used;
177 list_t _dl_stack_user;
178 list_t _dl_stack_cache;
179 size_t _dl_stack_cache_actsize;
180 uintptr_t _dl_in_flight_stack;
181 int _dl_stack_cache_lock;
182 #else
183 /* If loading a shared object requires that we make the stack executable
184 when it was not, we do it by calling this function.
185 It returns an errno code or zero on success. */
186 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
187 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
188 #endif
189 struct dl_scope_free_list *_dl_scope_free_list;
190
191 #ifdef NEED_DL_SYSINFO
192 /* Needed for improved syscall handling on at least x86/Linux. NB: Don't
193 initialize it here to avoid RELATIVE relocation in static PIE. */
194 uintptr_t _dl_sysinfo;
195 #endif
196 #ifdef NEED_DL_SYSINFO_DSO
197 /* Address of the ELF headers in the vsyscall page. */
198 const ElfW(Ehdr) *_dl_sysinfo_dso;
199
200 struct link_map *_dl_sysinfo_map;
201
202 # include "get-dynamic-info.h"
203 #endif
204 #include "setup-vdso.h"
205 /* Define the vDSO function pointers. */
206 #include <dl-vdso-setup.c>
207
208 /* During the program run we must not modify the global data of
209 loaded shared object simultaneously in two threads. Therefore we
210 protect `_dl_open' and `_dl_close' in dl-close.c.
211
212 This must be a recursive lock since the initializer function of
213 the loaded object might as well require a call to this function.
214 At this time it is not anymore a problem to modify the tables. */
215 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
216 /* This lock is used to keep __dl_iterate_phdr from inspecting the
217 list of loaded objects while an object is added to or removed from
218 that list. */
219 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
220 /* This lock protects global and module specific TLS related data.
221 E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
222 GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
223 accessed and when TLS related relocations are processed for a
224 module. It was introduced to keep pthread_create accessing TLS
225 state that is being set up. */
226 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
227
228
229 #ifdef HAVE_AUX_VECTOR
230 #include <dl-parse_auxv.h>
231
232 int _dl_clktck;
233
234 void
235 _dl_aux_init (ElfW(auxv_t) *av)
236 {
237 #ifdef NEED_DL_SYSINFO
238 /* NB: Avoid RELATIVE relocation in static PIE. */
239 GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
240 #endif
241
242 _dl_auxv = av;
243 dl_parse_auxv_t auxv_values;
244 /* Use an explicit initialization loop here because memset may not
245 be available yet. */
246 for (int i = 0; i < array_length (auxv_values); ++i)
247 auxv_values[i] = 0;
248 _dl_parse_auxv (av, auxv_values);
249
250 _dl_phdr = (void*) auxv_values[AT_PHDR];
251 _dl_phnum = auxv_values[AT_PHNUM];
252
253 if (_dl_phdr == NULL)
254 {
255 /* Starting from binutils-2.23, the linker will define the
256 magic symbol __ehdr_start to point to our own ELF header
257 if it is visible in a segment that also includes the phdrs.
258 So we can set up _dl_phdr and _dl_phnum even without any
259 information from auxv. */
260
261 extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
262 assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
263 _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
264 _dl_phnum = __ehdr_start.e_phnum;
265 }
266
267 assert (_dl_phdr != NULL);
268 }
269 #endif
270
271
272 void
273 _dl_non_dynamic_init (void)
274 {
275 _dl_main_map.l_origin = _dl_get_origin ();
276 _dl_main_map.l_phdr = GL(dl_phdr);
277 _dl_main_map.l_phnum = GL(dl_phnum);
278
279 _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
280
281 /* Set up the data structures for the system-supplied DSO early,
282 so they can influence _dl_init_paths. */
283 setup_vdso (NULL, NULL);
284
285 /* With vDSO setup we can initialize the function pointers. */
286 setup_vdso_pointers ();
287
288 /* Initialize the data structures for the search paths for shared
289 objects. */
290 _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
291 /* No glibc-hwcaps selection support in statically
292 linked binaries. */
293 NULL, NULL);
294
295 /* Remember the last search directory added at startup. */
296 _dl_init_all_dirs = GL(dl_all_dirs);
297
298 _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
299
300 _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
301
302 _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
303
304 _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
305 if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
306 _dl_profile_output
307 = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
308
309 if (__libc_enable_secure)
310 {
311 static const char unsecure_envvars[] =
312 UNSECURE_ENVVARS
313 ;
314 const char *cp = unsecure_envvars;
315
316 while (cp < unsecure_envvars + sizeof (unsecure_envvars))
317 {
318 __unsetenv (cp);
319 cp = strchr (cp, '\0') + 1;
320 }
321 }
322
323 #ifdef DL_PLATFORM_INIT
324 DL_PLATFORM_INIT;
325 #endif
326
327 /* Now determine the length of the platform string. */
328 if (_dl_platform != NULL)
329 _dl_platformlen = strlen (_dl_platform);
330
331 for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
332 switch (ph->p_type)
333 {
334 /* Check if the stack is nonexecutable. */
335 case PT_GNU_STACK:
336 _dl_stack_flags = ph->p_flags;
337 break;
338
339 case PT_GNU_RELRO:
340 _dl_main_map.l_relro_addr = ph->p_vaddr;
341 _dl_main_map.l_relro_size = ph->p_memsz;
342 break;
343 }
344
345 call_function_static_weak (_dl_find_object_init);
346
347 /* Setup relro on the binary itself. */
348 if (_dl_main_map.l_relro_size != 0)
349 _dl_protect_relro (&_dl_main_map);
350 }
351
352 #ifdef DL_SYSINFO_IMPLEMENTATION
353 DL_SYSINFO_IMPLEMENTATION
354 #endif
355
356 #if ENABLE_STATIC_PIE
357 /* Since relocation to hidden _dl_main_map causes relocation overflow on
358 aarch64, a function is used to get the address of _dl_main_map. */
359
360 struct link_map *
361 _dl_get_dl_main_map (void)
362 {
363 return &_dl_main_map;
364 }
365 #endif
366
367 /* This is used by _dl_runtime_profile, not used on static code. */
368 void
369 DL_ARCH_FIXUP_ATTRIBUTE
370 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
371 const void *inregs, void *outregs)
372 {
373 }